*2.2. Technology and Equipment for the Deposition of DLC Coatings on End Mills*

To apply DLCs to the surface of the end mills, they were placed on the turntable of the vacuum chamber of a hybrid technological unit (Figure 4), the design of which allows the sequential application of coatings in a single cycle by various methods: vacuum-arc deposition by evaporation of cathode materials (Arc-PVD); plasma-chemical gas-phase deposition in a glow discharge plasma by chemical reaction and decomposition of gas mixture components-plasma-enhanced chemical vapor deposition (PECVD). Two types of coatings were applied: (1) double-layer coatings consisting of an adhesive sublayer (CrAlSi)N and the outer DLC layer; (2) single-layer DLCs.

**Figure 4.** The principal application of DLC-coatings and (CrAlSi)N/DLC-coatings on end mills with the use of hybrid technology unit.

We used the original PI311 series technological unit developed by PLATIT AG (Selzach, Switzerland). The unit (Figure 4) is equipped with a gas filtration device and a multi-channel gas inlet system, a vacuum pumping system, a source of bias voltage to the turntable, and two cylindrical rotating cathodes made of chromium (Cr) and silumin (AlSi). For minimizing micro drops in the formed coating (CrAlSi)N, the unit implements the original lateral rotating cathodes (LARC) technical solution. This technology does not involve the use of bulky magnetic separators to minimize micro drops but uses rotating cathodes that are placed on the periphery of the chamber, and virtual gates that work without any mechanical elements. Following the generally accepted classification and terminology, the DLCs deposited in this work refer to hydrogenated diamond-like a-C: H films.

Preliminary cleaning of the cutters, which is necessary to achieve adequate strength of the adhesive bond of the deposited coating, was carried out with argon ions with an energy of 500 eV at a pressure of 1 Pa using a non-self-sustaining gas discharge ignited between the cathodes. At the same time, a negative voltage of 400 V was applied to the rotary table with the processed samples. The electron flow between the cylindrical cathodes created a high-density plasma, by which the samples were efficiently cleaned of impurities and oxides for 15 min before the deposition of the coating. After the cleaning was completed at a pressure of 1.5 Pa, gradually decreasing to 0.7 Pa, an adhesion sublayer (CrAlSi)N was formed by two Cr and AlSi cathodes when a gas mixture of nitrogen (volume fraction 90%) and argon (volume fraction 10%) and supplying negative voltage to the turntable of 500 V. The time of deposition of the (CrAlSi)N layer was 25 min, which provided a thickness of about 1.5 μm. Then the outer diamond-like layer was formed by plasma-chemical gas-phase deposition in a glow

discharge plasma by starting a chemical reaction and decomposing the components of the gas mixture supplied to the chamber: acetylene C2H2 (volume fraction 78%), argon Ar (volume fraction 7%), and tetramethylsilane Si(CH3)4 (volume fraction 5%). The deposition time of the diamond-like layer was 180 min, which provided a thickness of about 2.5 μm. For the application of a single-layer DLC, the process step associated with the formation of an adhesive sublayer was excluded, and after cleaning the cutters, the DLC layer was deposited directly. The DLC layer was deposited at a pressure of 4.0 Pa. This value's choice is because a decrease in this parameter leads to a decrease in the productivity of the process when an increase leads to an excessive increase in the structure of the graphite-like component's coating.

A Tescan VEGA3 LMH scanning electron microscope was used to analyze the structure of DLCs deposited using the technology described above.
